Benzene, toluene, and xylenes (BTX) are basic building blocks of modern petrochemical industries. The present source of these compounds primarily is the refining of petroleum. As petroleum supplies dwindle so does the supply of benzene, toluene and xylene. Alternative sources must be developed for these compounds. We have discovered a process for making benzene, toluene and xylene which utilizes materials which can be indirectly derived from a readily available source, synthesis gas.
Development of fossil fuel conversion processes has enabled the production of oxygenated hydrocarbons from coal, natural gas, shale oil, etc. Synthesis gas (CO+H.sub.2) is readily obtained from the fossil fuels and can be further converted to lower aliphtic oxygenates, especially methanol (MeOH) and/or dimethyl ether (DME). U.S. Pat. No. 4,237,063 (Bell et al) discloses the conversion of synthesis gas to oxygenated hydrocarbons using metal cyanide complexes. U.S. Pat. No. 4,011,275 (Zahner) discloses the conversion of synthesis gas to methanol and dimethyl ether by passing the mixture over a zinc-chromium acid or copper-zinc-alumina acid catalyst. U.S. Pat. No. 4,076,761 (Chang et al) discloses a process for making hydrocarbons from synthesis gas wherein an intermediate product formed is a mixture of methanol and dimethyl ether.
Processes for the conversion of coal and other hydrocarbons to a gaseous mixture comprising hydrogen and carbon monoxide, carbon dioxide, etc., are well known. Such a gaseous mixture hereinafter will be referred to simply as synthesis gas or syngas. An excellent summary of the art of gas manufacture, including synthesis gas, from solid and liquid fuels, is given in Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 10, pages 353-433, (1966), Interscience Publsihers, New York, N.Y., the contents of which are herein incorporated by reference.
It has recently been demonstrated that alcohols, ethers, carbonyl and their analogous compounds may be converted to higher hydrocarbons, particularly aromatics-rich high octane gasoline, by catalytic conversion employing shape selective medium pore acidic zeolite catalyst, such as H-ZSM-5. This conversion is described in U.S. Pat. Nos. 3,894,103, '104, '106; 3,928,483, 3,907,915 (Chang et al ); which describe oxygenate conver sion techniques suitable for converting methanol or the like. The process has become known as the methanol-to-gasoline or "MTG" process, and produces mainly C.sub.5 + gasoline range hydrocarbon products with C.sub.3 -C.sub.4 LPG and C.sub.9.sup.+ heavy aromatics. The desirable C.sub.6 -C.sub.8 BTX can recovered as a separate product slate by conventional distillation and extraction techniques. These light aromatics are also produces in a related process for converting methanol to olefins (MTO), as described in U.S. Pat. No. 4,011,278 (Plank et al); 4,550,217 (Graziani et al); 4,513,160, 4,547,616 (Avidan et al), incorporated herein by reference.
An object of this invention is to increase the yield of products rich in benzene, toluene, and xylenes (i.e. greater than 50 percent aromatics) when oxygenated hydrocarbons such as methanol and dimethyl ether and product streams containing these and other oxygenated hydrocarbon compounds are converted to hydrocarbons rich in benzene, toluene and xylene. Another object of this invention is to improve present methods of converting readily available oxygenates to products rich in benzene, toluene and xylenes.